Photobiomodulation inhibits neuronal firing in the superficial but not deep layer of a rat spinal dorsal horn

• Published in: Biochemical and biophysical research communications 2024-05, Vol.710, p.149873, Article 149873
• Main Authors: Uta, Daisuke, Ishibashi, Naoya, Tao, Shinichi, Sawahata, Masahito, Kume, Toshiaki
• Format: Article
• Language: English
• Subjects: Animals; Aβ fiber; In vivo extracellular recording; Lamina IV; Low-level laser therapy; Low-Level Light Therapy; Neurons; Pain; Photobiomodulation; Rats; Rats, Sprague-Dawley; Sciatic Nerve; Spinal Cord - physiology; Spinal Cord Dorsal Horn; Spinal dorsal horn
• ISSN: 0006-291X; 1090-2104; 1090-2104
• DOI: 10.1016/j.bbrc.2024.149873

Photobiomodulation (PBM) has attracted attention as a treatment for chronic pain. Previous studies have reported that PBM of the sciatic nerve inhibits neuronal firing in the superficial layers (lamina I–II) of the spinal dorsal horn of rats, which is evoked by mechanical stimulation that corresponds to noxious stimuli. However, the effects of PBM on the deep layers (lamina III–IV) of the spinal dorsal horn, which receive inputs from innocuous stimuli, remain poorly understood. In this study, we examined the effect of PBM of the sciatic nerve on firing in the deep layers of the spinal dorsal horn evoked by mechanical stimulation. Before and after PBM, mechanical stimulation was administered to the cutaneous receptive field using 0.6–26.0 g von Frey filaments (vFFs), and vFF-evoked firing in the deep layers of the spinal dorsal horn was recorded. The vFF-evoked firing frequencies were not altered after the PBM for any of the vFFs. The inhibition rate for 26.0 g vFF-evoked firing was approximately 13 % in the deep layers and 70 % in the superficial layers. This suggests that PBM selectively inhibits the transmission of pain information without affecting the sense of touch. PBM has the potential to alleviate pain while preserving the sense of touch. [Display omitted] •We examined the effects of photobiomodulation (PBM) on the spinal dorsal horn.•Firing was evoked by mechanical stimulation using von Frey filaments (vFFs).•Firing in the deep layers (lamina III–IV) of the spinal dorsal horn was unaffected.•The analysis of inhibition rate demonstrated PBM selectively inhibits superficial layer firing without affecting deep layer firing.